Storm water, which also is called urban runoff, is surface runoff of rainwater, melted snow or ice, wash water or similar from different types of surfaces. Such surfaces can be parking lots, sidewalks, roofs, and similar surfaces, sometimes referred to as impervious surfaces. Water running off from such surfaces tends to become polluted by e.g. gasoline, oil, heavy metals, trash, fertilizers, pesticides and other pollutants. During rain these surfaces carry polluted storm water to storm drains. Storm drains can be connected to a drainage system for discharge into receiving surface waters, such as a canal, river, lake, reservoir, sea, ocean, or other surface water, with or without treatment of the storm water before discharge.
Storm drains generally comprise a vertical pipe having an inlet, such as a horizontal grated inlet or a side inlet, being connected to a drainage system. Such storm drains commonly comprise a catch basin, also called sump or gully-pot, for catching small objects, such as sediment, sand, gravel, pebbles, twigs, trash and similar. Then, the catch basin serves as a water-filled trap for trapping objects and prevents such objects from entering the subsequent drainage system. Such catch basins also prevent gases from the drainage system from escaping out into the open air. Storm water from the top of the catch basin drains into the subsequent drainage system. The catch basins can be emptied by means of vacuum trucks at suitable time intervals in order to prevent clogging of the drainage system.
There are different types of devices for filtering storm water disclosed in the prior art. Such prior art devices commonly comprise a filter for positioning in an inlet of a storm drain. Commonly the filter unit is fixedly mounted or attached to the inlet of the storm drain in question. This approach results in a troublesome and time consuming installation process. Also the removal of the filter may be troublesome and time consuming. Moreover, the installation of a filter may reduce the capacity of the storm drain concerned.
EP 2 620 561 A1 discloses a floating filter device for filtering storm water inside a storm drain. The disclosed filter device uses various materials for removing pollutants or contaminants from the storm water being filtered. The disclosed device may suffer from stability problems when e.g. being subjected to large flows of storm water.
Hence, there is a need for an improved device for filtering storm water inside a storm drain.